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The Global Positioning System (GPS) is designed to estimate the locations of users or objects, and has a variety of civilian and military applications. Although angles-of-arrival (AOAs) may be required to enhance the desired GPS signals, it is difficult to estimate explicit AOA information because a GPS signal has a low power relative to the noise level. In this paper, we propose a GPS AOA estimation method based on a modified despreader and the constant modulus (CM) array cost function. This technique has a low computational complexity compared with other AOA estimation methods, such as the Multiple Signal Classification (MUSIC) algorithm, because it does not require a singular value decomposition (SVD). It also has good estimation performance in low signal-to-noise ratio (SNR) environments.

The multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) is one of core technologies for the third generation (3G) and fourth generation (4G) communication systems. The efficient channel estimation scheme with relatively low estimation error is required for the MIMO-OFDM communication system. In this paper, we propose a channel estimation scheme based on the adaptive algorithm such as the least-mean-square (LMS) and a preamble signal architecture considering the guard subcarrier, which is suitable to MIMO-OFDM. The proposed algorithm which estimates channels in the time-domain has not only the low channel estimation error but the low peak-to-average power (PAPR) comparing to conventional techniques such as the least-square (LS). Computer simulation results are provided to illustrate the performance of the proposed algorithm for the channel estimation.